In HSPA enabled WCDMA systems that use so called uplink closed loop beam forming, sometimes also referred to as uplink closed loop transmit diversity, a NodeB informs a beam forming capable UE of the beam forming that the UE should use. This is usually done by means of transmitting a code word to the UE which identifies a set of pre-coding weights (“a pre-coding vector”) in a code book. The pre-coding weights in the pre-coding vector are then used by the UE by using each pre-coding weight in the set for multiplication with information which is transmitted from one of the UE's antennas, i.e. the pre-coding vector comprises one pre-coding weight for each of the antennas.
In order for the NodeB to be able to determine a suitable pre-coding vector for a particular UE, the NodeB must have information about the radio channel conditions between the NodeB and the UE, information which is usually obtained by means of (multiple) pilot signals which are transmitted from the UE to the NodeB. The NodeB which determines the pre-coding vector for a UE is usually the UE's serving NodeB, although it can also in some cases be another NodeB or the UE's Radio Network Controller, its RNC.
As will be realized, it is advantageous if a pilot or sounding signal for HSPA WCDMA closed loop beam forming is designed so that the impact on WCDMA channelization code use, hardware complexity, signaling overhead, interference level, link and system performance and soft handover operation is optimized.